1902.] 



the Question of Blaze Currents. 



217 



and the posterior part of the eyeball are led off from, is sufficient to 

 suggest that the real seat of origin of the " blaze currents " is to be 

 sought for in the anterior part of the eye. Waller, who at first* 

 regarded the " blaze currents " as having their origin in the retina, 

 has in a subsequent! publication, stated that tissues, other than 

 retinal, take part in their production. 



Observations on Separate Parts of the Eyeball. 



If the posterior part of the eye alone is placed on the electrodes and 

 stimulated, the response is the same as in the whole eye when the 

 equator is led off from, i.e., only a very slight variation occurs. If 

 the anterior part of the eye is investigated by itself, the effects produced 

 are the same as when cornea and optic nerve are led off from. It 

 Avas, therefore, obvious that cornea, lens, and ciliary body must 

 next be investigated separately. One would especially expect to get 

 electromotive effects with the ciliary ring on account of the attached 

 iris and its muscles. Experiment showed that break and make 

 induction shocks in either direction always gave deviations and 

 excursions in a definite direction which cannot, however, be said to be 

 positive in relation to the resting current on account of the incon- 

 stancy of the latter, which is due, no doubt, to the irregular con- 

 struction of the organ. The preparation is, moreover, very perishable, 

 and very soon gives no effect at all, or only (polarisation X) effects, the 

 direction of which varies with that of the exciting current. 



The lens is much more easy to work with. From it one obtains, 

 according to the position of the electrodes, well-marked though weak 

 resting currents in a constant and definite direction. In response to 

 excitation, effects in one direction (the positive) occur whatever the 

 direction of the exciting current. They are frequently preceded by 

 negative initial jerks when the exciting current is in the same direc- 

 tion, just as is the case in the whole eye. Although the "blaze 

 currents " are in this case much stronger than they are in the ciliary 

 body, those of the two together are not nearly sufficient to account 

 for the currents in the whole eyeball. The only remaining part of 

 the eye in which to seek for the principal seat of origin of those large 

 differences of potential, which occur in the response of the whole eye, 

 was now per exclusionem the cornea, and, according to expectation, this 

 was found by experiment to give strong electromotiA'e effects. The 

 preparation was made by cutting into the eyeball at the edge of the 

 cornea with scissors, and then cutting right round the limbus. The 



* Waller. "On the Retinal Currents of the Frog's Eye, excited by Light and 

 exoil ed Electrically," ' Phil. Trans.,' B, vol. 193, p. 123. 



t " On the * Blaze Currents' of the .Frog's Eyeball," ' Phil. Trans.,' B, vol. 194, 

 p. 183. 



B 2 



